The present invention relates to a process for producing a titanium oxide. Specifically, the present invention relates to a process for producing a titanium oxide suitable for a photocatalyst.
It has been investigated that malodorous substances in air, or organic solvents or surfactants in water are decomposed and removed by a photocatalytic activity shown by titanium oxide. Recently, a decomposition and removal method using visible light as a light source has been studied owing to the wide usability and the convenience, and a titanium oxide exhibiting a high photocatalytic activity by irradiation of visible light has been developed.
Such a titanium oxide can be produced, for example, in an ion implantation method in which vanadium or chromium is introduced into titanium oxide. However, the ion implantation method needs a specific apparatus equipped with a vacuum container. In addition, there are problems in scaling up of the production apparatus or mass production thereof and, therefore, the production cost tends to be high.
One object of the present invention is to provide a process for easily producing a titanium oxide showing a high photocatalytic activity by visible light radiation without using a specific apparatus equipped with a vacuum container or the like.
This object and other objects are achieved by the present invention which provides a process for producing a titanium oxide. The process includes the steps of (i) mixing an acidic solution of a titanium compound with a nitrogen-containing basic organic compound to obtain a reaction product and (ii) calcining the obtained product.
A titanium oxide in the present invention is produced in a process which comprises the steps of (i) mixing an acidic solution of a titanium compound with a nitrogen-containing basic organic compound to obtain a reaction product and (ii) calcining the obtained product.
Examples of the acidic solution of a titanium compound include an aqueous solution of titanium trichloride (TiCl3), titanium tetrachloride (TiCl4), titanium sulfate [Ti(SO4)2.mH2O, 0xe2x89xa6mxe2x89xa620], titanium oxysulfate [TiOSO4.nH2O, 0xe2x89xa6nxe2x89xa620], titanium oxychloride (TiOCl2) and the like. The acidic solution of a titanium compound may be prepared in a suitable known method such that a titanium compound is dissolved in water, or that a titanium oxide or a titanium hydroxide is dissolved in a mineral acid such as sulfuric acid and hydrochloric acid. The content of titanium compound in the acidic solution may be about 1% by weight to about 40% by weight in terms of titanium atom.
In the present invention, the nitrogen-containing basic organic compound to be mixed with the above-described acidic solution of a titanium compound may be a compound containing nitrogen atom in its molecule and having basic properties. Examples of the nitrogen-containing basic organic compound include amines such as an acyclic amine, an alicyclic amine and an aromatic amine. The nitrogen-containing basic organic compound may be used singly or in the combination of two or more of them.
The acyclic amine which may be used in the present invention is a compound having at least one amino group in its molecule. Examples thereof include primary monoamines which have a chemical formula CnH2n+1NH2 wherein n represents an integer of from 1 to 10, primary diamines which have a chemical formula of H2NCnH2nNH2 wherein n represents an integer of from 1 to 10, dialkylamines having 2 to 10 carbon atoms, trialkylamines having 3 to 10 carbon atoms and the like. More specifically, examples of the acrylic amine include methylamine, ethylamine, n-propylamine, n-butylamine, iso-propylamine, sec-butylamine, ethylenediamine, 1,3-propanediamine, 1,2-propanediamine, dimethylamine, diethylamine, trimethylamine, triethylamine and the like.
The alicyclic amine which may be used in the present invention is a compound having at least one amino group, wherein the amino group is directly connected with a carbon atom of the aliphatic ring of the amine, or an aliphatic, heterocyclic compound having at least one nitrogen atom in the aliphatic ring. The alicyclic amine may have a heteroatom such as oxygen atom and sulfur atom in the aliphatic ring. Also, the alicyclic amine may have an aliphatic hydrocarbon group, alicyclic hydrocarbon group, an aromatic hydrocarbon group, an acyl group or the like, or additionally have a substituent such as an amino group through the above-described group. More specifically, examples of the alicyclic amine include cyclohexylamine, cyclohexanediamine, pyrrolidine, piperidine, pipecoline, piperazine, N-methylpiperazine, N-ethylpiperazine, N-propylpiperazine and the like.
The aromatic amine which may be used in the present invention is a compound having at least one amino group, wherein the amino group is directly connected with a carbon atom of the aromatic ring, or an aromatic, heterocyclic compound having at least one nitrogen atom in the aromatic ring. The aromatic amine may have a heteroatom such as oxygen atom and sulfur atom in the aromatic ring. Also, the aromatic amine may have an aliphatic hydrocarbon group, alicyclic hydrocarbon group, an aromatic hydrocarbon group, an acyl group or the like, or additionally have a substituent such as an amino group through the above-described group. More specifically, examples of the aromatic amine include aniline, phenylenediamine, pyridine, pyrimidine, 4-aminopyridine, melamine and the like.
The mixing of an acidic solution of a titanium compound with a nitrogen-containing basic organic compound may be conducted in any suitable method. For example, the nitrogen-containing basic organic compound is added into the acidic solution of the titanium compound, or the acidic solution of the titanium compound is added into the nitrogen-containing basic organic compound. The mixing is preferably conducted at a low temperature. The temperature may be about 60xc2x0 C. or lower, preferably about 40xc2x0 C. or lower and more preferably about 10xc2x0 C. or lower.
The ratio of the nitrogen-containing basic organic compound to the acidic solution of the titanium compound may be about 0.5 time or more, preferably about 0.8 time or more, and about 10 times or less, preferably about 3 times or less, in terms of the base equivalent of the nitrogen-containing basic organic compound based on the acid equivalent of the acidic solution of the titanium compound. The acid equivalent is the molar amount multiplied by the valence of acid groups contained in the acidic solution of the titanium. The base equivalent is the molar amount of basic nitrogen atom contained in the nitrogen-containing basic organic compound. For example, the basic equivalent of a monoamine is one equivalent per one mole thereof whatever the monoamine (such as a primary, secondary or thirdly amine) is. The basic equivalent of a diamine is 2 equivalent per one mole thereof.
The resulting product thus obtained by the mixing of the acidic solution of the titanium compound with the nitrogen-containing basic organic compound is then calcined. The calcination is preferably carried out in the atmosphere having an oxygen content of from about 1% by volume to about 10% by volume. For example, the calcination is preferably carried out in a mixed gas of oxygen and nitrogen or a mixed gas of air and an inert gas such as nitrogen, each mixed gas having a prescribed content of oxygen. Although not outside the scope of the present invention, when the calcination is carried out in the atmosphere having an oxygen content of more than about 10% by volume, the photoactivity of the obtained titanium oxide may be decreased. Also again while not outside the scope of the present invention, when the calcination is carried out in the atmosphere having a oxygen content of less than about 1% by volume, the photoactivity of the obtained titanium oxide may be decreased. The temperature of the calcination may be about 300xc2x0 C. or higher, and be preferably from about 350xc2x0 C. to about 600xc2x0 C.
In the present invention, a particulate titanium oxide may be produced. The particulate titanium oxide can be used as a photocatalyst as it is. Alternatively, the particulate titanium oxide may be mixed with a suitable bonding agent and then be molded to be utilized as the molding article thereof. Also, the particulate titanium oxide may be utilized for being applied onto a variety of construction materials, automobile materials or the like, or for coating such materials. In the applying or coating, the particulate titanium oxide may be used in a coating agent which is obtained by dispersing the titanium oxide in a solvent such as water, alcohols and ketones, or by peptizing the titanium oxide with an acid.
The titanium oxide of the present invention may be used as a photocatalyst, for example, as follows:
The titanium oxide may be put in a visible-light-transmitting glass tube or container together with a liquid or gas to be treated, and then be irradiated with visible light having a wavelength of 430 nm or more using a light source. In the irradiation of visible light to the titanium oxide, the liquid or gas in the tube or container may be oxidized, reduced or decomposed. Irradiation time of light may be determined depending on light intensity of the light source, and the kind and amount of the liquid or gas to be treated. The light source is not particularly limited as long as it can emit visible light having a wavelength of 430 nm or more. Example of the light source include solar rays, a fluorescent lamp, a halogen lamp, a black light, a xenon lamp, a mercury arc lamp and a sodium lamp. The light source may be equipped with an ultraviolet-cutting filter and/or an infrared-cutting filter, if necessary.
As described above, in accordance with the present invention, the titanium oxide exhibiting a high photocatalytic activity with radiation of visible light can be easily produced.
The process for producing titanium oxide of the present invention is described in Japanese application no. 2000-279500, filed on Sep. 14, 2000, the complete disclosures of which are incorporated herein by reference.
Also, the invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are to be regarded as within the spirit and scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be within the scope of the following claims.